This disclosure relates generally to electrical current detection devices and, more specifically, to an electrical current detection device for coaxial cables.
Referring to FIG. 1, a typical hybrid fiber coax (HFC) broadband network that combines optical fiber and coaxial cable requires grounding of the subscriber premise coaxial network. This is usually accomplished through a coaxial splice connector at the outdoor junction device (J), which includes means to attach a ground wire that is subsequently terminated to the ground connection of the premise electrical service.
For electrical current to flow, there must be a return path back to the source. In a home or premise, the source is the power company's distribution transformer (T), and the path for the return current is the power company's neutral conductor (N). However, there are occurrences when the utility power company's neutral connection is weakened by corrosion or poor mechanical splicing, illustrated at Premise A. In the event of a loose or open neutral connection, the current will seek the path of least resistance. Often, this path is through the cable company's ground conductor because it is tied into the power company's neutral connection. As can be seen by the arrows, the coaxial cable (C) can become the conducting means to complete the current of the in-home A/C electrical service.
In the illustrated example, the return current flows backwards through the cable ground wire to the outdoor junction device, through the braid of the coax cable to the cable company's distribution box (D), to the Premise B junction device, and then through premise B's neutral conductor back to the transformer (T).
The amount of current that flows through the coaxial cable varies depending on the severity of the loss of the power utility neutral connection. Small amounts of current may not pose a direct electrical shock hazard, but will introduce undesired levels of upstream ingress into the coax network. In extreme cases, the current will melt the coax cable, resulting in loss of cable service or sparks/shock while connecting the drop coax to the cable plant.
When a loose or open neutral conductor is suspected, a clamp-on ammeter can be used by knowledgeable personnel to confirm the high sheath current condition. Although this detection method can be useful and may be advantageous for certain applications, it suffers from drawbacks. For example, loss of service and damage to the cable has already occurred. Furthermore, most cable technicians do not carry and are not trained to use a clamp-on ammeter.